Consider a cellular network that consists of one BS serving a set \(\mathcal {K}\)  of \(K\)  users, as shown in Fig. REF .
Each user \(k\)  has a local dataset \(\mathcal {D}_k\)  with \(D_k\)  data samples.
For each dataset \(\mathcal {D}_k=\lbrace x_{kl},y_{kl}\rbrace _{l=1}^{D_k}\) , \(x_{kl}\in \mathbb {R}^d\)  is an input vector of user \(k\)  and \(y_{kl}\)  is its corresponding outputFor simplicity, this paper only considers
an FL algorithm with a single output. Our approach can be extended to the
case with multiple outputs [1]}..
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